How can the nanocrystallinity of 7 nm spherical Co nanoparticles dispersed in solution be improved?

We report a solution-phase annealing of spherical Co nanocrystals synthesized in reverse micelles and coated with dodecanoic acid. The deposition of a drop of solution on a transmission electron microscope grid shows that a progressive increase in the temperature to 316 °C results in the progressive crystallographic transition from a polycrystalline and probably face-centered cubic Co phase to the single-crystalline hexagonal close-packed (hcp) Co phase. These nanocrystals are highly stable against oxidation and coalescence. We stress that, to our knowledge, this constitutes the first example in the literature of pure hcp-Co spherical single crystals dispersed in solution. These nanocrystals can be freely manipulated and, due to their low size dispersion, can self-organize on various substrates.     

QND measurements using dual ported cavities

 Optical QND measurements may be made using devices which act as nonlinear beam splitters, transmitting noise in a phase-sensitive way. One class of such devices are resonant optical cavities containing a nonlinear medium. By appropriate choice of nonlinearity and operating parameters, various QND observables may be measured. We consider, in particular, the extent to which the QND performance of these devices is degraded by intracavity losses. Received: 8 March 1996     

A Simple Method to Prepare Alkyl 3,5-Dioxohexanoates

A simple and efficient method to prepare alkyl 3,5-dioxohexanoates by alcoholysis of isopropylidene (1-hydroxy-3-oxo-butylidene) malonate is described.     

Influence of uniaxial draw on near-surface structure in poly(ethyleneterephthalate)

Relative amounts of surface crystallinity and amorphous structure and their respective surface orientations were examined as a function of depth from the surface for a series of uniaxially drawn poly(ethyleneterephthalate) (PET) films using polarized attenuated total-reflectance infrared spectroscopy (ATR-IR). Qualitative depth resolution on a scale from ca. 0.5 to 5 μm is obtained. The results indicate a higher degree of extended trans segments and a higher degree of extended trans orientation near the surface in the machine direction, relative to the bulk film. These quantities also increase with increasing uniaxial draw ratio. No evidence for orientation of the gauche conformer at the surface as a function of uniaxial draw ratio is observed. All conclusions are consistent with the presence of increased crystallinity at the surface of the films. Increases in trans structure and orientation measured by ATR-IR measurements are consistent with bulk crystallinity measurements from density and x-ray scattering measurements.     

Bistability and photon antibunching in sub/second harmonic generation

We analyse the nonlinear interaction between a fundamental and second harmonic wave inside a Fabry-Pérot cavity where both modes are driven by a coherent driving field with a definite phase. We find that under certain experimentally accessible conditions bistable operation is possible. In addition it is shown that photon antibunching in the steady state may occur.     

The projection geometry of the field-ion image

An expression for the projection geometry of the field-ion microscope is derived and it is shown how a single parameter describing the projection relationship may be obtained from measurements on the micrograph. The relationship of experimentally obtained projections to the stereographic case is discussed, as is the influence of varying emitter radius.     

Dispersive optical bistability in a ring cavity

Equations governing the behaviour of a single mode high-Q ring cavity are obtained for a coherent driving field (detuned to both cavity and atoms) and inhomogeneously broadened atomic transitions using a Hamiltonian approach. We find the region of bistability and critical points in the homogeneous broadening case. Numerical results including inhomogeneous broadening show that bistability is obtained more readily by detuning both the atomic transition and the cavity mode relative to the driving field.     

A coherent nonlinear mechanism for optical bistability from three level atoms

A novel scheme for optical bistability in a coherently driven three level atomic system is proposed. The scheme utilizes the non absorption resonance which occurs due to a population trapping in a coherent superposition of the ground state sublevels. The resulting optical bistability occurs for a lower threshold power than for a two level system and is insensitive to Doppler and laser bandwidth effects.